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Stephen T. Garnett and Les Christidis (2007). Implications of changing
species definitions for conservation purposes. Bird Conservation
International, 17, pp 187-195. doi:10.1017/S0959270907000809.
Bird Conservation International (2007) 17:187–195. ß BirdLife International 2007
doi: 10.1017/S0959270907000809 Printed in the United Kingdom
Implications of changing species definitions for
conservation purposes
STEPHEN T. GARNETT and LES CHRISTIDIS
Summary
Concern has been expressed that failure to adopt phylogenetic or related species concepts will
result in biodiversity loss. Here we describe how widespread adoption of such concepts may
affect conservation administration and the social contract with elected governments that fund
management of threatened species. We then review threatened species legislation, showing that
most laws and international conventions avoid arguments over species’ definitions altogether,
thus negating arguments that such definitions should be changed to further species’
conservation.
Introduction
The definition of species is at once one of the most fundamental and one of the most ephemeral
concepts in biology. While the importance of taxonomy has been magnified since ratification of
the Convention on Biological Diversity (Samper 2004), this has not helped end the search for a
universal definition of species (see Padial and de la Riva 2006 for references). The initial purpose
of Western taxonomy was to order biological diversity (Linnaeus 1758), and, until the twentieth
century, the species was the first step in a hierarchy stretching up to kingdom, each step an
accumulation of information on physical similarity expressed by the step before. In the
twentieth century the foundations of this largely artificial structure were cemented in place by
the Biological Species Concept (Mayr 1969). It was believed that the species was a mooring to
which the confusion of life could be anchored.
Initially it had been hoped that genetics would provide definitive evidence of disputed species
boundaries. Alas there was no elixir in genetic differentiation that separated species from other
levels in the hierarchy – species became a stutter in the continuum of genetic diversity from gene
to landscape rather than the single unarguable step. And the more that is known about genetic
variation, the greater the confusion of statistical hierarchies that can be created with the
information. The point at which phylogenetic hierarchies should be deconstructed into the
category of species often seems to be a function of the choice of statistical models (e.g. Holder et
al. 2005) and the portion of DNA (e.g. Rubinoff and Holland 2005) analysed.
This has affected species definitions. Many are in circulation (Mayr 1969, Wiley 1981,
Paterson 1985, Ridley 1989, Templeton 1989, Nixon and Wheeler 1990, Committee on Scientific
Issues in the Endangered Species Act 1995, Mallet 1995, Staley 1997, Blaxter 2004).
Microbiologists, for instance, simply set an arbitrary level of overlap in DNA, 70%, to define
species. By this definition, chimpanzees and humans belong to a single species. As it is, only
6,000 species of bacteria have been described, none of which are threatened (Staley 1997, Ohren
2004). However, among complex organisms, the biological (BSC) and phylogenetic (PSC) species
concept currently dominate debate (Isaac et al. 2005). The BSC is built around existing patterns
of real or assumed reproductive behaviour, with forms being distinguished as species if there is a
lack of free interbreeding (Mayr 1969). Thus, in birds, interspecific barriers can be porous (e.g.
S. T. Garnett and L. Christidis
188
Grant and Grant 2002), with natural interspecific hybridization being relatively common,
particularly among parapatric species (Randler 2006). Even intergeneric reproduction is
commonplace in plants (Knobloch 1972). However, the different forms can be considered as
species if mating is assortative. Where geographical isolation makes reproductive incompatibility
impossible to prove, species rank is identified through comparison with similar sympatric species
pairs (Mayr 1969).
The PSC deals with these same issues by recognizing species on the basis that populations
need to be distinguishable only on differences in one taxonomic character and that there is ‘‘a
parental pattern of ancestry and descent’’ (Cracraft 1989), even though the PSC populations
sometimes meet, hybridize and become indistinguishable (Helbig et al. 2002, Gow et al. 2006).
Although such an approach could simplify taxonomic decisions, it renders the concept in an
operational, not theoretical, sense comparable to the typological concept of nineteenth-century
systematists (Haffer 1992, Christidis and Boles 1994). The PSC is operationally and conceptually
virtually indistinguishable from the subspecies rank of the BSC. The evolutionary species
concept (ESC; Wiley 1978, Wiley and Mayden 2000, Peterson 2006, 2007), by which
independent evolutionary trajectories are assessed on the basis of a largely subjective
consideration of the degree of morphological and genetic divergence, has the same result.
Since most subspecies were described in a pre-statistical era, the PSC or ESC merely add a formal
framework not previously available (Remsen 2005). Thus a phylogenetic subspecies concept
could indeed be useful, especially given the inconsistency with which such entities are currently
defined (Zink 2003), but the application of the concept to species results merely in the loss of
information about evolutionary relationships and degrees of separateness.
However, despite shortcomings of the PSC, it has proved popular in well-studied groups such
as primates (Groves 2001) and, to a lesser extent, birds (e.g. Cracraft 1992, Robertson and Nunn
1998, Holdaway et al. 2001). This application of the PSC has led to an increase in the number of
new ‘‘species’’, dubbed ‘‘taxonomic inflation’’ (Isaac et al. 2004). Because these new ‘‘species’’
inevitably have smaller distributions and populations than those from which they were derived,
this greatly increases the number of species that meet IUCN Red List criteria for being
threatened. Given these consequences, we think that two aspects of the discussion about species
concepts warrant further comment: the implication that taxonomy can be used to advance
conservation of threatened species, and the possible impact of adopting the PSC on conservation
investment.
Are conservation imperatives influencing taxonomy?
Species are embedded in Western consciousness because, in any one place, most biological
entities interbreed only with their own kind. The concept is widely understood; deriving from
concepts arrived at through observation before formal Western taxonomy arose. We contend
that public concern about biodiversity loss, which has resulted in political acceptance that
biodiversity conservation is something in which public monies should be invested, is primarily
concern for loss of species. The most recent evidence of this is acceptance of the IUCN Red Lists
as measures of human progress towards meeting the Millennium Goals (BirdLife International
2007a). As Mace (in Marris 2007) observed, policy-makers and legislators believe strongly in the
species concept whatever either taxonomists or conservation biologists may think about its
merits. Furthermore we contend that this belief, and the concomitant investment in species
conservation, assumes that the definition of species is based on objective principles and is not
being manipulated to attempt to increase that investment.
Penhallurick and Wink (2004) contended that the main factor driving the splitting of albatross
species in Robertson and Nunn (1998) was that conservation legislation in many countries where
albatrosses breed and feed considers only species worthy of protection. Whatever the truth of
this assertion, the perception that the PSC had been adopted for conservation objectives can
damage both conservation and taxonomy. So too can statements that a failure to adopt the PSC
Implications of changing species definitions for conservation purposes
189
is threatening species with small ranges (Hazevoet 1996), even if this is just a case of
taxonomists being misunderstood (Sangster 2000). The rise in popularity of the PSC has
certainly coincided not just with greater understanding of genetics but also with the fear of
species extinction. Although it is obviously important that taxonomists and conservation
biologists collaborate (Rojas 1992, Mace 2004), we fear that creating more species out of existing
entities, inevitably with smaller ranges, could be perceived as a form of scientific dishonesty. If
taxonomic changes are to be made for political reasons, then those elected to make political
decisions have a right to participate in the debate.
This is partly because any shift to a PSC and a sudden surge in new species has implications
for broader society beyond just conservation. Although the legal implications of changing species
definitions may be surprisingly small (see below), each time the name of a species changes, or
species boundaries are redefined, a huge bureaucratic process is triggered to update schedules,
regulations, maps and publications. This has both transaction and opportunity costs, the former
because substantial conservation monies are spent negotiating the new lists through the
administrative processes, and the latter because those funds might have been available for
genuine on-ground conservation. This is not to suggest the vigour of taxonomic endeavour
should be reduced. The enthusiasm for the PSC that is driving taxonomic inflation in mammals
and some other groups (Isaac et al. 2004) is in fact masking a surge in new species descriptions in
groups such as the amphibians, most of which have been identified using conventional BSC
taxonomic techniques (Padial and de la Riva 2006). Nor do we find fault with the systematic
application of conventional techniques to reveal bird species hidden among existing entities
(Watson 2005). Rather we advocate consistency in the amount of evidence required before new
entities are created that warrant the attention of government investment. We believe that to
expand lists of species en masse to reflect a new species concept about which only a subset of
taxonomists agree, is to place the social commitment to threatened species conservation at risk
for dubious benefit. Wholesale changes to species lists dissipate resources and political
enthusiasm and have little benefit for conservation on the ground.*
Taxonomy, legislation and Red Listing
Curiously the bureaucratic activity that attends shifting taxa from subspecies to species actually
influences very little with respect to the implementation of conservation legislation. If
Robertson and Nunn (1998) did split the albatrosses for conservation reasons (Penhallurick and
Wink 2004), they did so unnecessarily. In fact, for the most part, the people drafting
international agreements or national legislation have carefully avoided defining ‘‘species’’ in any
way that takes sides in the scientific debate (Table 1). None of the conventions or laws
encountered in creating Table 1 state definitively that taxa below the level of species are to be
ignored (although sometimes whole classes can be excluded, e.g. fish were deliberately omitted
from the definition of vertebrates under the Territory Parks and Wildlife Conservation Act in
Australia’s Northern Territory). Most explicitly include subspecies and populations. Although
Annex five to the CITES convention (CITES 2007) does say species and subspecies are defined
using the BSC, stating innocently that ‘‘‘species’ and ‘subspecies’ refer to the biological concept
of a species, and do not require any further definition’’, it then explains how even populations
can be included under its provisions. National legislation is equally inclusive, especially that
written recently. The Philippine Wildlife Resources Conservation and Protection Act (RA 9147)
2001, for instance, specifically mentions that it includes subspecies, thus potentially easing
Peterson’s (2006) concern for several Philippine taxa not conventionally recognized as species.
Among Western countries the legislation in which least guidance is given on definitions appears
*
The debate has extended beyond scientific forums since this paper was accepted for publication; The
Economist notes that it ‘‘behoves taxonomists to be honest. If they debase their currency, it will ultimately
become valueless’’ (Anon 2007).
S. T. Garnett and L. Christidis
190
Table 1. Definitions of species or their equivalent in a selection of international conventions and legislation
aimed at species conservation. Countries were selected on the basis that legislation was readily available in
English, to provide examples from all continents and across a spectrum of wealth.
Convention/Legislation (source)
International conventions
Convention on Biological Diversity
(www.biodiv.org)
Wording in relation to species
Article 2: ‘‘Biological diversity’’ means the variability
among living organisms from all sources including, inter
alia, terrestrial, marine and other aquatic ecosystems and
the ecological complexes of which they are part; this
includes diversity within species, between species and of
ecosystems
Convention on the Conservation of Migratory Article 1.1.a: ‘‘Migratory species’’ means the entire
Species of Wild Animals (www.cms.int)
population or any geographically separate part of the
population of any species or lower taxon of wild animals, a
significant proportion of whose members cyclically and
predictably cross one or more national jurisdictional
boundaries
Ramsar Convention on Wetlands
Criterion 6: A wetland should be considered internationally
(www.ramsar.org)
important if it regularly supports 1% of the individuals in
a population of one species or subspecies of waterbird
Criterion 7: …a significant proportion of indigenous fish
subspecies, species or families, life-history stages, species
interactions and/or populations …
Criterion 9: …it regularly supports 1% of the individuals
in a population of one species or subspecies of wetlanddependent non-avian animal species
Convention on International Trade in
Article 1 (a): ‘‘Species’’ means any species, subspecies, or
Endangered Species of Wild Fauna and Flora geographically separate population thereof
(www.cites.org)
Annex 5 to Resolution Conf. 9.24: ‘‘Species’’ and
‘‘subspecies’’ refer to the biological concept of a species, and
do not require any further definition
‘‘Geographically separate population’’ refers to parts of a
species or a subspecies within particular geographical
boundaries. This can also refer to populations or
subpopulations, or, for the sake of convenience in certain
cases, to ‘‘stocks’’’ as the term is understood in fisheries
management
Convention on the Conservation of European Article 4: Each Contracting Party shall take appropriate
Wildlife and Natural Habitat
and necessary legislative and administrative measures to
(conventions.coe.int)
ensure the conservation of the habitats of the wild flora and
fauna species, especially those specified in Appendices I and
II
Appendix II includes the subspecies Puffinus assimilis
baroli
National legislation
Australia
Section 528: ‘‘species’’ means a group of biological entities
Environmental Protection and Biodiversity
that: (a) interbreed to produce fertile offspring; or (b)
Conservation Act 1999 (www.austlii.edu.au)
possess common characteristics derived from a common
gene pool; and includes: (c) a sub-species; and (ca) for the
purposes of Part 13A – a distinct population of such
biological entities; and (d) except for the purposes of Part
13A– a distinct population of such biological entities that
the Minister has determined, under section 517, to be a
species for the purposes of this Act
Implications of changing species definitions for conservation purposes
191
Table 1. Continued.
Convention/Legislation (source)
Wording in relation to species
Canada
Species at Risk Act 2002 (laws.justice.gc.ca)
Section 2(1): ‘‘wildlife species’’ means a species, subspecies,
variety or geographically or genetically distinct population
of animal, plant or other organism, other than a bacterium
or virus, that is wild by nature
Chile
Title 1, Article 2: Biodiversity or biological diversity: the
General Bases of the Environment 1994. Law variability of organisms alive that form part of all
(www.cochilco.cl)
terrestrial and aquatic ecosystems. It includes diversity
within the same species, between species and between
ecosystems
China
Wildlife protected under this Law refers to the species of
Law of the People’s Republic of China on the terrestrial and aquatic wildlife which are rare or near
extinction and the species of terrestrial wildlife which are
Protection of Wildlife 2004
(www.enviroinfo.org.cn)
beneficial or of important economic or scientific value
England and Wales
Wildlife and Countryside Act 1981
(www.jncc.gov.uk)
India
Wildlife (Protection) Act 1972 (envfor.nic.in)
New Zealand
Wildlife Act 1953
Conservation Act 1987
(www.legislation.govt.nz)
Philippines
Wildlife Resources Conservation and
Protection Act (RA 9147) 2001
(www.grain.org)
South Africa
National Environmental Management:
Biodiversity Act 2004 (www.info.gov.za)
Thailand
Wild Animal Reservation and Protection
Act – BE. 2535 1992 (chanyakomol.com)
USA
Endangered Species Act 1973 (www.fws.gov)
Part 1, Section 2: ‘‘wild animal’’ means any animal (other
than a bird) which is … living wild;’’
‘‘wild bird’’ means any bird of a kind which is ordinarily
resident in or is a visitor to Great Britain in a wild state …
Provide[s] for the protection of [Wild animals, birds and
plants]
Chapter 1. Section 2 (1): ‘‘animal’’ includes amphibians,
birds, mammals, and reptiles, and their young, and also
includes, in the cases of birds and reptiles, their eggs
Section 2 (1): Wildlife means any animal that is living in a
wild state
Section 1, 2 (1): Animal means any member of the animal
kingdom other than a human being
Ch.2.Section 5 (x): ‘‘Wildlife’’ means wild forms and
varieties of flora and fauna, in all developmental stages,
including those which are in captivity or are being bred or
propagated
Sections f,h,i,o,w refer to ‘‘species and subspecies’’ of
wildlife
Ch.1 Part 1 (1): ‘‘species’’ means a kind of animal, plant or
other organism that does not normally interbreed with
individuals of another kind, and includes any sub-species,
cultivar, variety, geographic race, strain, hybrid or
geographically separated population
Section 4: ‘‘Wildlife’’ means all kinds of animals including
terrestrial, aquatic, and winged animals as well as insects,
which by nature are born and live in the forest or water
Section 3 (16): The term ‘‘species’’ includes any subspecies
of fish or wildlife or plants, and any distinct population
segment of any species or vertebrate fish of wildlife which
interbreeds when mature
to be the Bern Convention and the compliant European legislation, at least from England and
Wales. However, the Bern Convention schedules includes one subspecies among the protected
‘‘species’’, which implies that subspecies are contained within its definition of species.
Species do have higher prominence at the IUCN, which has devolved responsibility for
defining the species concept among birds to BirdLife International, which holds firmly to the
BSC (BirdLife International 2007b). However, threatened subspecies can be assessed under the
S. T. Garnett and L. Christidis
192
IUCN criteria (IUCN 2001), and in the IUCN Red List (IUCN 2006) subspecies analyses are
available for some mammals, plants, reptiles and insects. Subspecies assessments have not been
provided for birds by the Red List Authority for birds, BirdLife International, primarily because
there is a lack of resources to undertake a comprehensive assessment (Butchart 2005).
Nowhere, however, is the IUCN listing adopted into legislation and many wealthy countries
have assessed the status of all subspecies of birds and listed those threatened under legislative
schedules. Thus it tends to be the poorer countries, many of which are highly subspeciose, where
subspecies assessment has not been undertaken. This leads to two related questions. First, would
elevating subspecies to species under the PSC lead to official IUCN Red Listing? Second, given
there is already provision for protecting subspecies under most local laws, will a lack of IUCN
listing make a difference to investment in their conservation?
The answer to the first question is probably yes, in time, if comprehensive widely accepted
taxonomic treatments using the PSC were available. As it is BirdLife recognizes that
conventional revision of the taxonomy of places such as east Asian archipelagos will reveal
more species than are currently recognized (BirdLife International 2007b).
The answer to the second question is far less certain. Although instability of species lists does
make it difficult to understand macro-ecological processes, to identify concentrations of
endemism with certainty, and to prioritize the allocation of conservation funds to hotspots (Isaac
et al. 2004), conservation investment dollars in known hot spots based on analyses using the
BSC are already stretched. Among birds, 20% of threatened species are not represented in
protected areas (Rodrigues et al. 2004) and only 67% had received some conservation action
during 2000–2004 (BirdLife International 2004). Conventional taxonomic revision is already
adding to this burden as the BSC is applied more carefully. Universal application of the PSC
could overwhelm the process yet protect entities that are only marginally different from those
already being considered. Certainly BirdLife International is concerned that a full listing of
subspecies or comprehensive PSC analysis could lead to diversion of limited conservation
resources away from threatened full species, together with the assumption that a large
proportion of threatened subspecies are likely to be benefiting by conservation action directed at
species (S. Butchart in litt.).
In contrast, in those wealthy countries where subspecies are recognized as entities that ought
to be conserved, the definition of taxa as subspecies has been no impediment to attracting
political and financial support. A third of all funds allocated to threatened bird conservation in
Australia in the period 1992–1999 were spent on threatened subspecies of species that had a
status of Least Concern (Garnett et al. 2003). In the United Kingdom nearly all funds are spent
on populations of species at the edge of their extensive European or Palaearctic ranges. The
timber industry in north-western United States has been turned inside out on account of the
northern subspecies of Spotted Owl Strix occidentalis caurina. Sadly, and tellingly for
proponents of the PSC, not all investment in subspecies can been justified. Recent analyses of
subspecies on the American mainland suggest that definitions of subspecies based on
morphology alone are unreliable, and that substantial public funds have been invested in
protecting entities whose taxonomic merit is questionable (e.g. Zink 2003).
Conclusion
For birds the BSC remains the most widely accepted taxonomic standard around the world. To
promote the PSC, or indeed the ESC, on the basis that it is better for conservation is to risk
alienating public trust in taxonomy as an objective science. Further there seems to be little
practical merit in adopting the PSC for conservation purposes. National and international
legislation has cannily avoided any definition that excludes entities that could be identified as
species using the PSC. Although the global IUCN Red List has not so far considered all
subspecies or distinct populations, adoption of the PSC in the IUCN Red List would incur
substantial transaction and opportunity costs while having only marginal benefit for biodiversity
Implications of changing species definitions for conservation purposes
193
conservation. As it is, countries that can afford to protect subspecies, or populations that are
defined as species only using the PSC, will do so. Where funding is more limited, conservation
efforts are likely to be concentrated on species that are defined conservatively.
Acknowledgements
This paper had its origins in a conversation with Nigel Collar and Ali Stattersfield of BirdLife
International in 2002. The first author was also given advice by his host at the time, Andrew
Balmford of the University of Cambridge Zoology Department. The paper has benefited in
review from comments by Stuart Butchart, Gabriel Crowley, Adam Drucker, Lincoln Fishpool,
Townsend Peterson, Peter Ryan, Van Remsen and an anonymous referee.
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S. T. GARNETT*
School for Environmental Research, Charles Darwin University, Darwin NT, 0909 Australia.
L. CHRISTIDIS
Australian Museum, Sydney, NSW, 2010 Australia and Department of Genetics, University of
Melbourne, Parkville, Vic3052, Australia.
*Author for correspondence. e-mail: [email protected]
Received 17 March 2007; revision accepted 23 May 2007